Aromatic polycyanates which are thermosettable to polytriazines are known, for example, from U.S. Pat. Nos. 3,448,079; 3,553,244; 3,694,410; 3,740,348; 3,755,402; 4,094,852 and 4,097,455. Said polytriazines possess excellent heat resistance, however, an improvement in their mechanical properties, especially tensile and flexural strength, tensile and flexural modulus and tensile elongation while maintaining or even increasing glass transition temperature, would be desirable. The present invention provides a method for improving one or more of the aforementioned properties by incorporation into the polymer chains of the polytriazines one or more rodlike mesogenic structure(s). Incorporation of said rodlike mesogenic structures can lead to a molecular level ordering of the polytriazine thermoset thereof. The present invention also provides polymerizable mixtures containing one or more of the polycyanates (polycyanamides) containing rodlike mesogenic structure(s) with, for example, one or more polycyanates (polycyanamides) which do not contain rodlike mesogenic moieties, epoxy resins, polymaleimides, polyamines, polyphenols, polymerizable ethylenically unsaturated compounds, compounds which simultaneously contain both a cyanate or cyanamide group and a polymerizable ethylenically unsaturated group, compounds which simultaneously contain both a 1,2-epoxide group and a polymerizable ethylenically unsaturated group, compounds which simultaneously contain both a maleimide group and a cyanate or cyanamide group and materials which contain one or more rodlike mesogenic structure(s) and an average of one cyanate or cyanamide group per molecule. The thermoset compositions prepared from the aforementioned polymerizable mixtures typically possess improvements in physical and mechanical properties relative to those thermoset compositions prepared using polycyanates (polycyanamides) which do not contain rodlike mesogenic structure(s).
Certain of the polycyanates containing rodlike mesogenic structure(s) exhibit novel thermally induced self-curing behavior at onset temperatures much lower than those encountered with the polycyanates which do not contain rodlike mesogenic structure(s). Two distinct variations of this modified curing behavior are provided: As a specific example, when the azomethine group (--CH.dbd.N--) is present as a rodlike mesogenic structure, it can lower the onset temperature to curing without participating in the formation of the curing structure of the thermoset product. As a second example, when the secondary amide group (--NH--CO--) is present, it too can lower the onset temperature to curing, but appears to participate in the formation of the curing structure of the thermoset product via reaction of the amide proton. When used as a component in the polymerizable mixtures of the present invention, these same polycyanates can often be used to reduce the onset temperature required to cure (thermoset) said mixture.